Explain to me fuel efficiency

[TurboRA28]

Hi all, can someone help my simple mind understand a fuel efficiency question...

I have a 80 series landcruiser, around 3tonne with a 1fz 4.5ltr petrol engine running a manual box. It uses around 25ltrs per 100km on average (mix of town and freeway).

Old man has a Toyota Coaster, 1uzfe with autobox. This weighs 4tonne and is the shape of a brick. It uses around 14ltrs per 100km on average.

The Coaster out performs the 80 series in every which way that I can see. Apart from low down torque.

So why can the 1fz be so thirsty and the 1uz not so? Even when it has another 1 tonne to lug around.

[river]

Hi,

Gearing?

seeyuzz
river

[oldcorollas]

effiiciency in it's most basic sense = energy used.

in practice it is a function of (roughly)
(weight + rolling resistance + air resistance ; vehicle speed + vehicle acceleration) x engine efficiency
the main detractor is vehicle weight and acceleration, unless you are only doing highway speeds.

do you accelerate faster more often than your old man? sit in traffic more?

internally the 1UZ is more likely to be more efficient in terms of losses, and probably more efficient at turning fuel into motion as well, but that large a difference is more likely down to driving style and losses through 4WD system/tyres?

edit: go on a roadtrip with both, accel the same, go same speed, and see if the difference is so great (maybe even swap drivers )

[sleepy1g]

well said oldcorollas

[MWP]

The Landcruiser also has a big gearbox, transfer case, big diffs, etc which decreases efficiency.

Hmm, i thought the 1FZ would be more efficient since its a straight 6 which is the ideal engine configuration?

Anyway, it probably mostly comes down to engine tune.
There might be bad sensors, etc which could be effecting tune.
What you need is a wideband O2 kit that you can check both cars with during normal driving.

[Toy77]

Hey Joel,

Is yours a constant 4wd model? i know there are kits to remove this from the landcruisers. What size tyres are you running on the cruiser? On my patrol going from factory 31 x 10.5 in to 285/75/16 (33x11.5 in) cost me around 2L per 100km.

Your consumption is in the right kind of ball park for a 4x4 of that size. I get around 20l / 100 in my patrol on petrol (25/100 on gas) but have gotten as bad as 24l per 100 and as good as 17l per 100km. this is all on road driving. the good figures were before i lifted it, and fitted the bigger tyres.

Cheers
Stew

[Rodger]

I get 13-14lt/100 from my Turbo diesel 80 series around town. And on a long road trip have gotten 10 per 100 for a total of 1450kms.
I have heard and been told by others that the Petrol 80 Series is simply notorious for fuel consumption straight from the factory anyway, but not as bad as 25lt/100.

Good autos can be more efficient as they keep the engine in its torque range, matching throttle position and changing gears more efficiently.

Driving style, service history, fuel quality, age (vehicle or otherwise) could all contribute.

Regards

Rodger

[Norbie]

Old man has a Toyota Coaster, 1uzfe with autobox. This weighs 4tonne and is the shape of a brick. It uses around 14ltrs per 100km on average.

Are you sure about this? The 2 tonne luxobarges normally found with 1UZ's don't do much better than that. Seems a bit optimistic for a 4 tonne box.

[thechuckster]

guess: the coaster is probably geared well down in the diff (it did previously have an asthmatic 4cyl engine?) so it gets up to speed with 'fairly limited' load on the motor - then once it's cruising, closed loop kicks in helping the numbers a bit?

[RyleyMA61]

yes, tune, torque delivery and LOAD are the big factors. aerodynamic force is proportional to speed squared, so if you're only around town and low speeds etc it won't make much difference

an engine that can produce more power can also result in better fuel economy- the same work required to accelerate a mass can be done easier without loading the engine more. 4WD will add load

im not really adding anything that hasn't been solved already.

as mentioned the straight 6 is balanced in the 1st, 2nd, 3rd (and more, i cant remember) harmonic, making it a very smooth engine (like V8s, V12s etc) but doesn't mean it's more ideal/efficient

physically larger engines are more efficient due to the heat transfer and friction- the larger transfer areas, the less friction and heat transfer. (ie the larger the pistons)

check tyre pressures? can severely affect rolling resistance

[CrUZida]

Are you sure about this? The 2 tonne luxobarges normally found with 1UZ's don't do much better than that

Err yes they do.
Normal consumption is 10L/100km's at those speeds
I've personally achieved mid 9's with the AC on.
Some have claimed mid 8's.

14L/100km's is only with 100% city driving.

[Norbie]

Normal consumption is 10L/100km's at those speeds

At what speeds? The OP didn't specify.

14L/100km's is only with 100% city driving.

Again the OP didn't say what mix of city/highway driving the Coaster was doing. Clarification is needed.

Even for 100% highway driving I think 14L/100km is a bit optimistic, given the huge frontal area and poor aerodynamics of a bus.

[lexsmaz]

I think some engines are inheritantly bad in design & subsequently have high fuel consumption, possibly due to poor & or old combustion chamber design, lack of ignition timing that can be used before detonation occurs .. Poor / low compression ratio etc, again governed by head design ...

I have a 80 series landcruiser with a 1fz 4.5ltr petrol engine. It uses around 25ltrs per 100km on average.

Backs up my thoughts as to why someone would even own a 4WD that lived in Suburbia, jeez at that consumption rate you would even think twice about driving down to the corner store ....

( No offence meant ) ....

[kickstartRA28]

I certainly couldnt afford a 4WD with that type of fuel consumption.

[CrUZida]

At what speeds? The OP didn't specify.

Ahh, indeed he didn't. I thought I saw 100kph somewhere, but it was L/100km's.

Again the OP didn't say what mix of city/highway driving the Coaster was doing. Clarification is needed.

Even for 100% highway driving I think 14L/100km is a bit optimistic, given the huge frontal area and poor aerodynamics of a bus.

Granted and agreed, but my comment was purely directed at your comment saying stock ones rarely achieve those figures.